PL217798B1 - Luminescent material and process for the preparation thereof - Google Patents

Abstract

The subject of the invention is a luminescent material characterized by the fact that it contains a matrix of lutetium trioxide Lu2O3 doped with praseodymium and hafnium, and a method for obtaining the said material.

Description

The number of known phosphors with the ability to permanently store the energy obtained during irradiation with high-energy ultraviolet or X-ray radiation is very limited. Among the known X-ray memories practically in medical imaging, only BaFBr: Eu ²⁺ powder has found application and is considered to be the best material of this type ever discovered. In 1980, Fuji Photo Film (Tokyo, Japan) patented a process that used a variety of photostimulated phosphors, including BaFX: Eu ²⁺ (X = Cl, Br), to record an image of the intensity of X-rays falling on a layer of such material (N. Kotera, S Eguchi, J. Miyahara, S. Matsumoto, and H. Kato, US patents US 4,236,078 and US4239968). In 1983, the method of obtaining a computer radiological image with the use of BaFBr: Eu ²⁺ X-ray memory was described in the literature. This phosphor remains the most extensively researched and refined phosphor of this type to this day (M. Sonoda, M. Takano, J. Miyahara, and H. Kato, Radiology 148 (1983) 833-838.). The possibility of producing transparent sheets based on Lu ₂ O ₃ has been described, inter alia, in A. Lempicki et al. Nucl. Instr. Meth A 488 (2002) 579-590. Information on the luminescence Lu ₂ O ₃ : Pr has already been published (C. De Mello Donega, A. Meijerink, G. Blasse, J. Phys. Chem. Solids 56 (1995) 673-685), but there is no mention of possibilities of energy storage in Lu2O3 based systems: Pr.

The disadvantage of all X-ray memories produced in the form of powders is the strong scattering of light on the phosphor grains. This phenomenon causes a strong blurring of medical images, one of the most important practical applications of this type of material. Therefore, attempts are made to produce X-ray memories in the form of transparent plates. To achieve this, optical memory crystalline grains are dispersed as small as possible in the glass matrix to further reduce scattering effects (S. Schweizer, J. A. Johnson, Radiation Measurements 42 (2007) 632-637). While the resolution of images obtained with the use of such X-ray memory is clearly better, the presence of glass - inactive in the emission generation process, but absorbing X-rays - makes it necessary to increase the dose of ionizing radiation, and this reduces the sense of such a solution in medical diagnostics. . After all, the main advantage of using X-ray memories in medical imaging was the significant reduction of the necessary dose of X-rays, which made the technique safer for the patient. The presented problem is solved by the present invention.

The subject of the invention is an optical and X-ray memory characterized in that it comprises a matrix of LU2O3 lutein trioxide doped with praseodymium and hafnium. Preferably, the memory according to the invention is characterized in that the praseodymium content, calculated in atomic percentages with respect to the lutetium, is from 0.025% to 0.2%. The memory according to the invention is likewise preferably characterized in that the hafnium content, based on atomic percentages with respect to the lutetium, is from 0.05% to 0.5%.

The second subject of the invention is a method of obtaining the optical and X-ray memory defined in the first aspect of the invention by the sol-gel technique, characterized in that it comprises the following steps: a) hydrated lutetium nitrate is mixed with a solution of a hydroxycarboxylic acid, preferably lemon, in the presence of metal ions of praseodymium and hafnium and ethylene glycol in stoichiometric ratios; b) heating the reaction mixture, preferably to about 80 ° C, to convert the mixture to a gel; c) heating the gel, preferably to 150 ° C, to convert into a resin; d) heating the resin, preferably to a temperature in the range 600-700 ° C, to burn the organic components to metal oxides; e) the material obtained in step d) is annealed to burn the organic components for 2 to 5 hours in a reducing gas atmosphere, preferably a 75:25 volumetric nitrogen / hydrogen mixture, vacuum or air at a temperature not lower than 1200 ° C; f) the material obtained in step e) is cooled. Equally preferably, the method according to the invention is characterized in that the metal ions used in the step of mixing the lutetium nitrate with the α-hydroxycarboxylic acid solution are in the form of metal oxides such as: Pr6O11, Lu2O3 or their salts, preferably chlorides, such as: HfCl4, nitrates, or other soluble in the citric acid used.

The most important advantage of the present invention is the fact that this phosphor has the highest density among known optical memories, and thus absorbs X-rays most effectively. This in turn means that, even in the form of a thin layer, it is able to absorb a larger fraction of the incident X-ray than other known optical and X-ray memories.

PL 217 798 B1

This, in turn, makes it possible to obtain higher light intensity during heating or stimulation of the material with infrared radiation. Another advantage of the presented optical and X-ray memory of great importance is the fact that this material can be produced not only in the form of a powder or a simple sinter, but also as a transparent ceramic sinter, due to the fact that it is an optically isotropic material as it crystallizes in a regular crystallographic system. Thanks to this, in the process of information retrieval as a result of stimulation with infrared or long-wave red radiation, light does not scatter. When used in medical diagnostics, this translates directly into an increase in image resolution and their contrast - the two most important parameters determining the quality and usefulness of a medical image. The observed light emission from the phosphor that is the subject of the present application is related to the radiation relaxation of the excited Pr ³⁺ ion. The emitted light is red, which is effectively recorded by a number of electronic detectors - photomultipliers, and especially photodiodes and CCD cameras. An important advantage of the presented material is also the fact that Lu2O3 does not show degradation of properties under the influence of atmospheric factors such as moisture, carbon dioxide and other gases present in the air. Thanks to this, it can be used without the need to use special protection against external factors. Materials capable of long-term storage of energy obtained as a result of absorption of short-wave radiation, e.g. ultraviolet radiation, can be used as X-ray detectors in digital medical diagnostics (digital imaging), in which the image "is evoked by stimulating the material previously exposed to X rays, the so-called X-ray memory, low-energy infrared or long-wave red radiation. Such materials can also be used in the security of sensitive documents and banknotes. They can also be used as temperature sensors. These materials, previously exposed to ultraviolet or X radiation, can also be used as a source of visible radiation when heated to higher temperatures or as a result of stimulation with infrared radiation. Fine-grained powders of such phosphors embedded in, for example, a polymer matrix can serve as an indicator of infrared laser radiation, which substantially increases the safety of working with infrared lasers. High density, and thus a high X-ray absorption coefficient by Lu2O3 and the possibility of producing it in the form of a transparent ceramic sinter, make medical diagnostics indicate the potential main use of Lu2O3 X-ray memory: Pr, Hf.

Examples of the implementation of the invention are shown in the attached drawing, in which Fig. 1 shows the emission spectrum under the influence of excitation by ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.025%), Hf (0.05%) synthesized at a temperature of 1700 ° C in air, Fig. 2 emission spectrum under the influence of X-ray excitation for Lu2O3: Pr (0.025%), Hf (0.05%) synthesized at a temperature of 1700 ° C in air, Fig. 3 glow curve recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.025%), Hf (0.05%) synthesized at a temperature of 1700 ° C in air, Fig. 4 glow curve recorded after exposure to X-ray radiation for Lu2O3: Pr (0.025%), Hf (0.05%) synthesized at a temperature of 1700 ° C in air, Fig. 5 optically stimulated luminescence (a) and its disappearance (b) recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.025%), Hf (0.05%) synthesized at a temperature of 1700 ° C in the air, a before the measurement of the irradiated ultraviolet radiation with a wavelength of 254 nm, Fig. 6, the glow curve recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at a temperature of 1700 ° C in the mixture atmosphere 25 % H2 + N2, Fig. 7 glow curves recorded for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a 25% H2 + N2 mixture after prior exposure to ultraviolet radiation with a wavelength of 254 nm ( solid line) and additionally after irradiation with infrared radiation with a wavelength of 980 nm (dash-dot line), 780 nm (dotted line) and after waiting 6 hours after exposure to UV radiation with a wavelength of 254 nm (dashed line), Fig. 8 curves incandescence recorded after exposure to X-ray radiation for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a mixture of 25% H2 + N2, Fig. 9 temperature dependence of luminescence ji recorded after exposure to X-ray radiation for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a mixture of 25% H2 + N2, Fig. 10 emission spectra recorded at temperatures of 100 ° C (dotted line) , 200 ° C (dashed line) and 270 ° C (solid line) after excitation with X-ray radiation for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at a temperature of 1700 ° C in the atmosphere of the mixture

PL 217 798 B1

25% H2 + N2, Fig. 11 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.025%), Hf (0.05%) synthesized at the temperature

1700 ° C in the atmosphere of a 25% H2 + N2 mixture, and before the measurement of the irradiated X-ray radiation, Fig. 12 disappearance of the afterglow at 160 ° C for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at the temperature of 1700 ° C in the atmosphere of a mixture of 25% H2 + N2. The experimental curve can be well described by the equation I = I ₀ * (1 + yt) ^-n , where γ = 2.74 * 10 ^-6 , and the value of the exponent n = 2.3, Fig. 13 the glow curve recorded after exposure to ultraviolet radiation of the length wave 254 nm for Lu2O3: Pr (0.05%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a 25% H2 + N2 mixture, Fig. 14, the temperature dependence of luminescence recorded after exposure to ultraviolet radiation of 254 nm for Lu2O3: Pr ( 0.05%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a mixture of 25% H2 + N2, Fig. 15 glow curve recorded after exposure to X-ray radiation for Lu2O3: Pr (0.05%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a mixture of 25% H2 + N2, Fig. 16 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.05%), Hf (0.1%) synthesized at a temperature of 1700 ° C in the atmosphere a mixture of 25% H2 + N2, and before the measurement of the irradiated beam X-ray radiation, Fig. 17 afterglow decay recorded at various temperatures: 160 ° C, 185 ° C, 200 ° C for Lu2O3: Pr (0.05%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a 25% H2 mixture + N2. The experimental curve can be well described by the equation I = I ₀ * (1 + γυ ^-η , where the values of the exponents ni γ change with the measurement temperature and are respectively n = 2.8, 5.7, 8.3 and γ = 9.11 * 10 ^-8 , 4.91 * ^10-8 , 1.14 *

10 ^-15 for 160 ° C, 185 ° C and 200 ° C, Fig. 18 emission spectrum under X-ray excitation for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at 1500 ° C in air, Fig 19 glow curve recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at 1500 ° C in air, Fig. 20 glow curve recorded after exposure to X-ray radiation for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at 1500 ° C in air, Fig. 21 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at the temperature 1500 ° C in air, and before the measurement irradiated with ultraviolet radiation with a wavelength of 254 nm, Fig. 22 emission spectrum under the influence of X-ray excitation for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at a temperature of 1500 ° C in a vacuum , Fig. 23 glow curve of zar recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at a temperature of 1500 ° C in a vacuum, Fig. 24 glow curve recorded after exposure to X-ray radiation for Lu2O3: Pr (0.05% ), Hf (0.2%) synthesized at 1500 ° C in a vacuum, Fig. 25 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.05%), Hf (0.2%) synthesized at 1500 ° C at vacuum, and before the measurement of irradiated with ultraviolet radiation with a wavelength of 254 nm, Fig. 26 emission spectrum under X-ray excitation for Lu2O3: Pr (0.05%), Hf (0.3%) synthesized at a temperature of 1700 ° C in a vacuum, Fig. 27 glow curve recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.05%), Hf (0.3%) synthesized at a temperature of 1700 ° C in a vacuum, Fig. 28 glow curve recorded after radiation exposure X-ray method for Lu2O3: Pr (0.05%), Hf (0.3%) synthesized at 1700 ° C in a vacuum, Fig. 29 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.05%), Hf (0.3 %) synthesized at a temperature of 1700 ° C in a vacuum, and before the measurement of irradiated X-ray radiation, Fig. 30 decay of afterglow at a temperature of 160 ° C for Lu2O3: Pr (0.05%), Hf (0.3%) synthesized at a temperature of 1700 ° C in a vacuum , the experimental curve can be well described by the equation I = I ₀ * (1 + γυ ^-η , where γ = 1.09 * 10 ^-6 , an = 2.3, Fig. 31 emission spectrum under the influence of X-ray excitation for Lu2O3: Pr (0.05% ), Hf (0.5%) synthesized at a temperature of 1700 ° C in air, Fig. 32 glow curve recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.05%), Hf (0.5%) synthesized at a temperature of 1700 ° C in air, Fig. 33, the glow curve recorded after irradiation with re for Lu2O3: Pr (0.05%), Hf (0.5%) synthesized at 1700 ° C in air, Fig. 34 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.05%), Hf (0.5%) ) synthesized at a temperature of 1700 ° C in air, and before measurement when exposed to ultraviolet radiation with a wavelength of 254 nm,

PL 217 798 B1

Fig. 35 emission spectrum under the influence of X-ray excitation for Lu2O3: Pr (0.1%), Hf (0.2%) synthesized at 1700 ° C in air, Fig. 36 glow curve recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3 : Pr (0.1%), Hf (0.2%) synthesized at 1700 ° C in air, Fig. 37 glow curve recorded after exposure to X-ray radiation for Lu2O3: Pr (0.1%), Hf (0.2%) synthesized at 1700 ° C in air, Fig. 38 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.1%), Hf (0.2%) synthesized at a temperature of 1700 ° C in air, and before the measurement of irradiated with ultraviolet radiation 254 nm, Fig 39 Decay of optically stimulated emission by infrared radiation 980 nm for Lu2O3: Pr (0.1%), Hf (0.2%) synthesized at a temperature of 1700 ° C in air,

Fig. 40 afterglow decay at 160 ° C for Lu2O3: Pr (0.1%), Hf (0.2%) synthesized at 1700 ° C in air, the experimental curve can be well described by the equation I = I ₀ * (1 + γ) ^-η , where γ = 9.74 * 10 ^-8 , an = 2.9, Fig. 41 emission spectrum under the influence of excitation by ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.1%), Hf (0.3%) synthesized at 1500 ° C in vacuum, Fig. 42 The glow curve recorded after exposure to ultraviolet radiation of 254 nm for Lu2O3: Pr (0.1%), Hf (0.3%) synthesized at 1500 ° C in a vacuum, Fig. 43 optically stimulated luminescence recorded under the influence of infrared radiation 980 nm for Lu2O3: Pr (0.1%), Hf (0.3%) synthesized at 1500 ° C in a vacuum, and before the measurement of irradiated X-ray radiation, Fig. 44 disappearance of optically stimulated infrared emission for Lu2O3: Pr (0.1%), Hf (0.3%) synthesized at 1500 ° C in vacuum, Fig. 45 glow curve a, recorded after exposure to ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.2%), Hf (0.1%) synthesized at a temperature of 1600 ° C in the air, Fig. 46 glow curve recorded after exposure to X-ray radiation for Lu2O3: Pr (0.2 %), Hf (0.1%) synthesized at a temperature of 1600 ° C in the air, Fig. 47 emission spectrum under the influence of excitation with ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.2%), Hf (0.2%) synthesized at a temperature of 1200 ° C in H2 (25%) + N2 atmosphere, Fig. 48 glow curve recorded after exposure to ultraviolet radiation of 254 nm for Lu2O3: Pr (0.2%), Hf (0.2%) synthesized at a temperature of 1200 ° C in an atmosphere of 25% H2 + N2, Fig. 49 emission spectrum under the influence of excitation with ultraviolet radiation with a wavelength of 254 nm for Lu2O3: Pr (0.2%), Hf (0.5%) synthesized at 1000 ° C in a vacuum, Fig. 50 glow curve recorded after irradiation with ultraviolet radiation 254 nm for Lu2O3: Pr (0.2%) , Hf (0.5%) synthesized at 1000 ° C in a vacuum and Fig. 51 glow curve recorded 1 hour after exposure to ultraviolet radiation of 254 nm for Lu2O3: Pr (0.2%), Hf (0.5%) synthesized at 1000 ° C in a vacuum.

P r z k ł a d 1.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.025% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.05% also with respect to lutetium. The above material is prepared as follows: 1.9985 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00048 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00071 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at approximately 1700 ° C in air. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a cream powder or a sinter (if pressed before annealing). The resulting phosphor materials are characterized by the emission of Pr ³⁺ ions in the red range of the spectrum with bands in the range 590-675 nm as shown in Figure 1. This wide range of emission bands gives the samples a distinctive red color luminescence. The emission can be efficiently excited by ultraviolet (UV) radiation with a wavelength in the range of about 200-330 nm, as well as by X-rays. After turning off the sample exciting light, it emits red light for a few minutes, showing the effect of the so-called afterglow. This emission, however, is of low intensity, and it quickly ceases to be visible.

PL 217 798 B1

Figure 2 shows the emission spectrum recorded during the irradiation of the sintered ceramic with X-rays. As after exposure to ultraviolet radiation, the material is characterized by red luminescence.

Figure 3 shows how, after prior exposure to ultraviolet radiation with a wavelength of 254 nm, as a result of annealing the sample from room temperature to 500 ° C, the emission characteristic of Pr ³⁺ ions appears in specific temperature ranges, but not lower than about 70-80 ° C, i.e. clearly above room temperature. The strongest luminescence occurs when the temperature of the material reaches about 200 ° C.

Figure 4 shows the glow curve for the same material recorded after irradiation with X-rays. This result practically does not differ from the result obtained after exposure to ultraviolet radiation, which indicates that in both cases analogous processes of energy storage in the material take place, and that this energy can be released in the form of red emission of Pr ³⁺ ions as a result of thermal stimulation. Figure 5a shows optically stimulated luminescence (OSL) under 980 nm infrared radiation, a material previously exposed to ultraviolet radiation. The obtained spectrum is identical to the emission spectrum recorded during exposure to ultraviolet radiation with a wavelength of 254 nm presented in Figure 1. This result shows that the material irradiated with ultraviolet radiation accumulates energy, which can then be released in the form of red light photons by stimulation with low-energy radiation in the range of infrared electromagnetic spectrum. Thus, both infrared radiation and elevated temperature can be used as factors allowing the release of the energy stored in the material in the form of red radiation of Pr ³⁺ ions. There is enough of this energy to emit for about 20 seconds, as shown by the decay of OSL in Figure 5b.

P r z k ł a d 2.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.025% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.1% also with respect to lutetium. The above material is prepared as follows: 1.9975 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00048 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00142 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at a temperature of about 1700 ° C in a reducing atmosphere, preferably a mixture of nitrogen and hydrogen in a 3: 1 volume ratio. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the air oven. The resulting product is a white powder or a sinter (if pressed before annealing).

Figure 6 shows a glow curve for a material that was previously exposed to ultraviolet radiation with a wavelength of 254 nm. We observe three strong emissions as the material reaches 100 ° C, 200 ° C and 270 ° C, with the strongest luminescence occurring when the material temperature reaches 270 ° C.

Figure 7 shows the glow curves recorded for Lu2O3: Pr (0.025%), Hf (0.1%) synthesized at a temperature of 1700 ° C in an atmosphere of a 25% H2 + N2 mixture after prior exposure to ultraviolet radiation with a wavelength of 254 nm and additionally after exposure to infrared radiation with a wavelength of 980 nm, 780 nm and after 6 hours of exposure to UV radiation with a wavelength of 254 nm. It turns out that 6 hours after irradiation, the trap located at about 100 ° C was emptied, the signal at about 200 ° C has a slightly lower intensity compared to the curve measured immediately after irradiation, while the signal at about 270 ° C remains unchanged both after waiting 6 hours after exposure as well as immediately after exposure. Energy evacuation from the traps at 100 ° C and 200 ° C occurs after irradiation with infrared radiation with a wavelength of 980 nm. On the other hand, after irradiation with radiation with a wavelength of 780 nm, it is possible to completely release energy from traps located at 100 ° C and 200 ° C, and also largely at 270 ° C.

Figure 8 shows the glow curve for a material after it has been previously irradiated with x-rays. The thermoluminescence plot looks very similar to that recorded for an ultraviolet irradiated material as shown in Figure 6, however

The intensity is much higher after irradiation with X-rays. There is practically no emission below 70 ° C, which indicates that the material permanently stores its stored energy at room temperature. In turn, comparing Figure 8 with Figure 4, which differ in hafnium concentration (0.1 and 0.05) and atmosphere (25% H2 + N2 and air), we see that 0.1% Hf and reducing atmosphere cause a significant increase in emission intensity at 270 ° C.

Figure 9 shows the temperature dependence of the luminescence recorded after irradiation with X-rays. The graph clearly shows how the emission spectrum changes with temperature, especially the intensity relations between the bands located at 620 nm and 631 nm. At a temperature of about 270 ° C, the intensity ratio of these bands is 1: 1, while when the material reaches about 200 ° C, the band at 620 nm is clearly lower. In order to present in detail the influence of the temperature achieved by a given ceramic sinter on the luminescence, emission spectra at given temperatures were selected, as shown in Figure 10. As the temperature increases, the intensity ratio between the 595 nm and 631 nm bands, as well as 620 nm, decreases. and 631 nm. In turn, the intensity relations between the bands 631 nm, 650 nm and 663 nm do not change with the change of the material temperature.

Figure 11 shows the spectrum of optically stimulated luminescence under the action of 980 nm infrared radiation. The recorded emission spectrum is practically identical to the emission spectrum induced by X-ray radiation (presented in Figure 2), which indicates that infrared radiation can release the energy accumulated in the material - during X-ray irradiation - which migrates to Pr ³⁺ ions, excites them, and these return to the ground state by emitting photons of red light. There is so much energy accumulated in the material that it allows for about twenty seconds of light under the conditions of the experiment.

Figure 12 shows how the intensity of the red Pr ³⁺ ion emission decreases while the material temperature is kept constant at 160 ° C. When the relationship is presented in logarithmic scales, it is close to linear. More specifically, the dependence of log (I) on log (t) can be described by the equation I = I ₀ * (1 + yt) ^-n , in which the parameters γ and n are 2.74 * 10 ^-6 and 2.3, respectively.

P r z k ł a d 3.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.05% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.1% also with respect to lutetium. The above material is prepared as follows: 1.997 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00096 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00142 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at a temperature of about 1700 ° C in a reducing atmosphere, preferably a mixture of nitrogen and hydrogen in a 3: 1 volume ratio. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the air oven. The resulting product is a white powder or a sinter (if pressed before annealing).

Figure 13 shows the glow curve for this material after prior exposure to ultraviolet radiation. The maximum intensity is observed when the material reaches a temperature of about 210 ° C. At room temperature, the signal is zero, which indicates no energy migration from the energy traps, in which it accumulates, to Pr ³⁺ ions. By relating the intensity of the thermoluminescence to the mass of the tested sintered ceramic and comparing it with all the examples presented in the description, for example 3 we record the most intense glow curve (Figure 13). Figure 14 shows the temperature dependence of the material luminescence during annealing. The emission has the same spectral characteristics as radioluminescence and UV emission. Luminescence starts appearing when the material reaches about 100 ° C. Figure 15 shows the glow curve recorded after irradiation with X-rays. The thermoluminescence trace is the same as in Figure 13 when the material was irradiated with ultraviolet radiation. At room temperature, we do not observe any emission, but the most intense emission occurs when the material reaches approx. 200 ° C. It should be noted that the course of the thermoluminescence curve for compounds containing 0.05% Pr differs from the curve for compounds containing 0.025% Pr (both materials annealed in a reducing atmosphere). For higher concentrations of Pr

We observe the largest population of energy traps when the temperature of the material reaches approx

200 ° C, while for materials with a lower concentration of Pr at 270 ° C.

Figure 16 shows the spectrum of optically stimulated luminescence under 980 nm infrared radiation for a sintered ceramic previously irradiated with X-rays. The recorded emission spectrum is identical to the emission spectrum obtained during the thermoluminescence measurement. There is so much energy accumulated in the material that it allows for about twenty seconds of light under the conditions of the experiment. Figure 17 shows the disappearance of the red emission of Pr ³⁺ ions as the material reaches different temperatures (160 ° C, 185 ° C and 200 ° C). It turns out that depending on the temperature of the test compound, the value of the exponent n, which speaks about the kinetics of thermoluminescence, changes, at temperatures of 160 ° C, 185 ° C, 200 ° C, n is 2.8, 5.7, 8.3, respectively, and the coefficient γ is 9.11 * 10 ^-8 , 4.91 * 10 ^-12, and 1.14 * 10 ^-15 . The values of both values were determined on the basis of the mathematical equation I = I ₀ * (1 + γt) ^-n .

P r z k ł a d 4.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.05% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.2% also with respect to lutetium. The above material is prepared as follows: 1.995 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00096 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00284 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at approximately 1500 ° C in air. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a cream powder or a sinter (if pressed before annealing). Figure 18 shows a radioluminescence spectrum which shape is the same as the optically stimulated luminescence spectrum after exposure to X-rays for material containing a lower amount (0.1%) of hafnium (see Figure 16). This means that in this case we do not observe the influence of hafnium concentration on the shape of the emission spectrum.

Figure 19 shows the dependence of the thermally stimulated luminescence of the material in the temperature range from room to 500 ° C. Emission occurs above a temperature of 80 ° C. Compared to the above-mentioned examples, we observe a much lower intensity of luminescence during annealing. The material reaches its maximum thermoluminescence at a temperature of about 210 ° C. In turn, Figure 20 shows a glow curve for a material that has previously been exposed to x-rays. We do not register emissions at room temperature, but only above 90 ° C. The strongest emission is observed when the material reaches about 200 ° C. In the glow curve, we observe an additional band at a temperature of 150 ° C. The ceramic sintered at 1500 ° C has a much lower intensity of the glow curve than the material synthesized at higher temperatures. Figure 21 shows optically stimulated luminescence under the influence of 980 nm infrared radiation of a material previously exposed to ultraviolet radiation. The intensity of the optically stimulated luminescence is much lower compared to the materials annealed at higher temperatures (Figure 16). However, the material irradiated with ultraviolet radiation accumulates energy that can then be released in the form of red light photons by stimulation with low energy radiation in the infrared electromagnetic spectrum, and this emission lasts for about 15 seconds.

P r z k ł a d 5.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.05% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.2% also with respect to lutetium. The above material is prepared as follows: 1.995 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00096 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00284 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at about 1500 ° C under vacuum. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than

It is about 500 ° C, and preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a white powder or a sinter (if pressed before annealing).

Figure 22 shows an emission spectrum recorded during an exposure to X-rays. Comparing Figures 22 with 18, which differ only in the annealing atmosphere (vacuum, air), we see practically no changes in the shape and intensity of the emission. Figure 23 shows an glow curve for a sintered ceramic which was previously exposed to ultraviolet radiation with a wavelength of 254 nm. We observe three emissions as the material reaches 100 ° C, 200 ° C and 270 ° C, with the strongest luminescence occurring when the material temperature reaches 200 ° C. Compared to sinters heated at higher temperatures (1700 ° C), the intensity is much lower, while comparing with the sinters obtained at the same temperature (1500 ° C) but in air, we observe an increase in TL intensity after heating in a vacuum. On the other hand, after exposure to X-ray radiation (Figure 24), the intensity of the glow curve increased almost threefold in comparison with the TL trace after exposure to ultraviolet radiation. The shape of the glow curve for the ceramic sinter described in this example is very similar to the glow curve recorded for a ceramic sinter obtained in a vacuum (Figure 20).

Figure 25 shows the spectrum of optically stimulated luminescence recorded by infrared radiation of 980 nm. For materials obtained in both air (Figure 21) and vacuum (Figure 22), the spectra of optically stimulated emission are very similar.

P r z k ł a d 6.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.05% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.3% also with respect to lutetium. The above material is prepared as follows: 1.993 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00096 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00426 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at approximately 1700 ° C under vacuum. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the air oven. The resulting product is a white powder or a sinter (if pressed before annealing). Figure 26 shows a radioluminescence spectrum which shape is the same as the spectrum of optically stimulated luminescence after irradiation with X-rays (see Figure 29). Several bands ranging from 590 to 700 nm were recorded. Figure 27 shows the glow curve for a material that was previously exposed to ultraviolet radiation with a wavelength of 254 nm. We observe the most intense emissions when the material reaches 100 ° C, 200 ° C and 280 ° C, with the strongest luminescence occurring when the material temperature reaches 200 ° C. Figure 28 shows the glow curve for a material after it has been previously irradiated with x-rays. The thermoluminescence plot looks very similar to that recorded for a material exposed to ultraviolet radiation, but the signal intensity at 100 ° C is much lower after exposure to X-rays. Figure 29 shows the spectrum of optically stimulated luminescence under the action of 980 nm infrared radiation for a material previously irradiated with X-rays. The recorded emission spectrum is practically identical to the radioluminescence spectrum (presented in Figure 26), which indicates that infrared radiation can release the energy accumulated in the material - during X-ray irradiation - which migrates to Pr ³⁺ ions, excites them, and these come back. to the ground state by emitting photons of red light. There is so much energy accumulated in the material that it allows for about twenty seconds of light under the conditions of the experiment. Figure 30 shows how the intensity of the red Pr ³⁺ ion emission decreases while the material temperature is kept constant at 160 ° C. When the relationship is presented in logarithmic scales, it is close to linear. More specifically, the dependence of log (I) on log (t) can be described by the equation I = I ₀ * (1 + yt) ⁿ , where the parameters y and n are 1.09 * 10 ^-6 and 2.26, respectively.

PL 217 798 B1

P r z k ł a d 7.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.05% based on lutetium atoms and a co-admixture of hafnium with a concentration of 0.5% also with respect to lutetium. The above material is prepared as follows: 1.989 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00096 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00711 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at approximately 1700 ° C in air. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the air oven. The resulting product is a white powder or a sinter (if pressed before annealing). Figure 31 shows a radioluminescence spectrum, which shape is the same as that shown in Figure 26 for a compound with a lower hafnium concentration and obtained in a vacuum, however having an intensity almost twice as low. We observe red emission of praseodymium in the range from 600 to 675 nm, as well as a single, low intensity band at 510 nm.

Figures 32 and 33 show the glow curves for this material after prior exposure to ultraviolet and X-ray radiation, respectively. The maximum intensity is observed at a temperature of about 200 ° C. At room temperature, the signal is zero, which indicates no energy migration from the energy traps in which it accumulates to Pr ³⁺ ions. We also observe that the relatively high (0.5%) concentration of hafnium causes that the emission, which starts at approx. 80 ° C, disappears only when the material reaches the temperature above 200 ° C. In comparison with the compound synthesized under the same conditions, but with a lower hafnium concentration, in the analyzed example, we observe a decrease in the intensity of the glow curve. Figure 34 shows the spectrum of optically stimulated luminescence recorded by infrared radiation of 980 nm. The recorded emission spectrum is identical to the emission spectrum obtained during the thermoluminescence measurement. There is so much energy accumulated in the material that it allows for about twenty seconds of light under the conditions of the experiment.

P r z k ł a d 8.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.1% calculated in relation to lutetium atoms and a co-admixture of hafnium with a concentration of 0.2% also in relation to lutetium. The above material is prepared as follows: 1.994 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00193 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00284 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at approximately 1700 ° C in air. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a cream powder or a sinter (if pressed before annealing).

Figure 35 shows an emission spectrum recorded during an exposure to X-rays. We observe a group of bands in the region from 590 nm to 700 nm and one low-intensity band around 10 nm. This band of bands is responsible for the red emission of praseodymium in lutetium oxide. The radioluminescence intensity is comparable to that of the compound described in Example 5. Figure 36 shows the glow curve for a sintered ceramic that was previously exposed to ultraviolet radiation with a wavelength of 254 nm. We observe three major emissions as the material reaches 100 ° C, 200 ° C and 280 ° C, with the strongest luminescence occurring when the material temperature reaches 200 ° C. When the tested material reaches the temperature of 140 ° C, an additional, low-intensity emission appears. The intensity of the glow curve recorded after exposure to X-ray radiation for the same material drops twelve times, as shown in Figure 37. In turn, the emission that appears at 140 ° C is more visible after exposure to X-ray than after UV. Figure 38 shows the spectrum of optically stimulated luminescence recorded under the influence of infrared radiation of 980 nm for a sintered ceramic previously irradiated with ultraviolet radiation of 254 nm. The shape of this illumination is very similar to the radioluminescence shown in Figure 35, which indicates that infrared radiation can release the energy accumulated in the material - during exposure to ultraviolet rays, or X-ray - the energy that migrates to Pr ³⁺ ions, excites them, and they return to the ground state, emitting photons of red light. Figure 39 shows the decay of optically stimulated emission during irradiation with 980 nm radiation. This material collects so much energy that it allows for about 25 seconds of light under the conditions of the experiment. Figure 40 shows the decay of the red emission of Pr ³⁺ ions when the material temperature is 160 ° C. The curve can be well described mathematically by the equation I = I ₀ * (1 + γί) ^-η , where the parameters γ and n are respectively 9.74 * 10 ^-8 and 2.9.

P r z k ł a d 9.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.1% calculated in relation to lutetium atoms and a co-admixture of hafnium with a concentration of 0.3% also with respect to lutetium. The above material is prepared as follows: 1.992 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00193 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00426 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at about 1500 ° C under vacuum. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a white powder or a sinter (if pressed before annealing).

Figure 41 shows the emission spectrum recorded during an irradiation of a sintered ceramic with ultraviolet radiation with a wavelength of 254 nm. The spectrum of luminescence consists of a set of bands in the range from 590 nm to 700 nm and they are responsible for the red emission of praseodymium, Pr ³⁺ . In contrast, Figure 42 shows the glow curve for this material after its previous irradiation with ultraviolet rays. The glow curve consists of three signals at 100 ° C, 200 ° C and 275 ° C, but they are very weak. Figure 43 shows the spectrum of optically stimulated luminescence under the action of 980 nm infrared radiation. The recorded emission spectrum is practically identical to the emission spectrum induced by ultraviolet radiation (presented in Figure 41), which indicates that infrared radiation can release the energy accumulated in the material - during exposure to ultraviolet rays - which migrates to Pr ³⁺ ions, excites them, and these return to the ground state by emitting photons of red light. Figure 44 shows the decay of optically stimulated emission during irradiation with 980 nm radiation. There is so much energy stored in the material that it allows for about 25 seconds of light under the conditions of the experiment.

P r z k ł a d 10.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with a praseodymium admixture with a concentration of 0.2% based on lutetium atoms and a hafnium co-admixture with a concentration of 0.1% also with respect to lutetium. The above material is prepared as follows: 1.994 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00386 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00142 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at about 1600 ° C in air. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a cream powder or a sinter (if pressed before annealing). Figures 45 and 46 show the glow curves for this material after prior exposure to ultraviolet and X-ray radiation, respectively. In both cases, we observe three signals as the material reaches 100 ° C, 200 ° C and 270 ° C. It should be noted, however, that these signals, compared to the above-mentioned ones, are very weak, which is caused by too high concentration of praseodymium.

P r x l a d 11.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with the admixture of praseodymium with a concentration of 0.2% calculated in relation to lutetium atoms and

It is a co-admixture of hafnium with a concentration of 0.2% also in relation to lutetium. The above material is prepared as follows: 1.992 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00386 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00284 g of hafnium chloride, HfCl4, 1.3 ml of ethylene glycol, C2H6O2 and 13 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at a temperature of about 1200 ° C in a reducing atmosphere, preferably a mixture of nitrogen and hydrogen in a 3: 1 volume ratio. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a white powder or a sinter (if pressed before annealing).

Figure 47 shows the emission spectrum recorded during an irradiation of a sintered ceramic with ultraviolet radiation with a wavelength of 254 nm. A set of bands in the range from 590 nm to 700 nm was recorded, which generate a red emission of praseodymium, Pr ³⁺ . In contrast, Figure 48 shows the glow curve for this material after its previous irradiation with ultraviolet rays. We observe the signal when the material reaches about 350 ° C, however it has an intensity at the noise level, meaning that we hardly observe any emissions when the material is warmed from room temperature to around 500 ° C. The reason is the high concentration of praseodymium and too low temperature of synthesis.

P r z k ł a d 12.

The optical and X-ray memory according to the invention is a Lu2O3 lutetium trioxide matrix activated with a praseodymium admixture with a concentration of 0.2% calculated in relation to lutetium atoms and a hafnium co-admixture with a concentration of 0.5% also with respect to lutetium. The above material is prepared as follows: 1.986 g of lutetium nitrate, Lu (NO3) 3 * 5H2O, 0.00386 g of praseodymium nitrate, Pr (NO3) 3 * 6H2O, 0.00711 g of hafnium chloride, HfCl4, 1.29 ml of ethylene glycol, C2H6O2 and 12.9 ml citric acid, C6H8O7 is thoroughly mixed and heated. The resulting resin is burned in an oven at 600 ° C for 5 hours in air. The obtained powder can be pressed in a press under increased pressure, then the end product is a sintered ceramic. The material is then placed in an oven and annealed at about 1000 ° C under vacuum. Maintain the sample in the same atmosphere until it has cooled down to a temperature of not more than about 500 ° C, preferably less than about 300 ° C. After it has cooled down, the phosphor can be removed from the oven. The resulting product is a white powder or a sinter (if pressed before annealing).

Figure 49 shows the luminescence spectrum recorded during the irradiation of a sintered ceramic with ultraviolet rays with a wavelength of 254 nm. We observe a set of bands in the range from 590 nm to 700 nm, which are responsible for the red emission of praseodymium, Pr ³⁺ . Figure 50 shows the glow curve for a material after it has been irradiated with ultraviolet rays previously.

One signal was recorded ranging from 150 ° C to 350 ° C with a maximum at 250 ° C, but its intensity is relatively low. There is practically no emission below 150 ° C, which indicates that the material permanently stores its energy at room temperature. This conclusion is confirmed by the glow curve recorded one hour after the material was irradiated with UV rays, presented in Figure 51. The result obtained is similar to that obtained immediately after irradiation. This shows that the energy stored in the material is permanently stored in it, and it can be released by increasing the temperature to at least 150 ° C or by irradiating with infrared rays.

Claims (5)

CLAIMS 1. Optical and X-ray memory comprising a Lu2O3 lutetium trioxide matrix doped with praseodymium and hafnium. 2. Memory according to claim The method of claim 1, wherein the praseodymium content, calculated as atomic percent with respect to the dolutet, is from 0.025% to 0.2%. 3. Memory according to claim The method of claim 1 or 2, characterized in that the content of hafnium, calculated as atomic percent with respect to lutetium, is from 0.05% to 0.5%. 4. Method for obtaining optical and X-ray memory as defined in claims 1-3 by sol-gel technique, characterized in that it comprises the following steps: PL 217 798 B1 a) mixed hydrated lutetium nitrate with a solution of α-hydroxycarboxylic acid, preferably citric acid, in the presence of metal ions of praseodymium and hafnium and ethylene glycol in stoichiometric ratios, b) heating the reaction mixture, preferably to a temperature of about 80 ° C, to convert the mixture to a gel, c) heating the gel, preferably to 150 ° C, to transform it into a resin, d) the resin is heated, preferably to a temperature in the range of 600-700 ° C, to burn the organic components into metal oxides, e) the material obtained in step d) is annealed to burn the organic components for 2 to 5 hours in a reducing gas atmosphere, preferably a mixture of nitrogen and hydrogen in a volume ratio of 75:25, vacuum or air at a temperature not lower than 1200 ° C, f) the material obtained in step e) is cooled. 5. The method according to p. 4. The method according to claim 4, characterized in that the metal ions used in the step of mixing lutetium nitrate with the α-hydroxycarboxylic acid solution are in the form of metal oxides such as: Pr6O11, Lu2O3 or their salts, preferably chlorides such as: HfCl4, nitrates, or other soluble in the citric acid used .